1. Field of the Invention
The present invention relates to flexible pipe joints with which piping systems of fluid pipes, such as water pipes buried in the ground, can optimally absorb such external forces as shearing forces or bending moments in a direction perpendicular to the pipe axis that occur during earthquakes or differential settlement or the like, so that damage to the fragile portions of the piping system can be avoided. More specifically, the present invention relates to flexible pipe joints, in which a first pipe member provided with a partially spherical circumferential surface that protrude outward in radial direction can be bendably joined with a second pipe member provided with a partially spherical inner circumferential surface that can slide along the partially spherical outer circumferential surface of the first pipe member.
2. Description of the Related Art
There are two types of this kind of flexible pipe joint:    (A) In the flexible pipe joint of the type shown in FIG. 13, a spherical ring member 2 having a partially spherical outer circumferential surface 2a is passed through a pair of cut-out portions (see FIG. 3) that are formed at one end of a second pipe member 3 serving as a socket pipe and that oppose one another in radial direction. The spherical ring member 2 is inserted inside a partially spherical inner circumferential surface 3a formed at one end of the second pipe member 3 in a posture in which the radial direction of the spherical ring member 2 is substantially parallel to the pipe axis X of the second pipe member 3, and the spherical ring member 2 is swiveled inside the partially spherical circumferential surface 3a, changing its posture such that it becomes coaxial with the pipe axis X of the second pipe member 3 (see FIG. 4). Then, a first pipe member serving as an inserted pipe portion is inserted, slidably in the direction of the pipe axis X, into the spherical ring member 2, and a locking member 6 is fitted to a ring-shaped installation groove 5 formed at the front end of the outer circumferential surface of the first pipe member 1. The locking member 6 is substantially C-shaped with an expandable diameter, and limits the range over which the spherical ring member 2 and the first pipe member 1 can move relative to one another in the direction of the pipe axis X by abutting against end surfaces 4a and 4b, of a limiting groove 4 formed at an inner circumferential surface of the spherical ring member 2, that are arranged in opposition in the direction of the pipe axis X.    (B) In the flexible pipe joint of the type shown in FIG. 14, a spherical pipe portion 1A having a partially spherical outer circumferential surface 1d is formed integrally at one end of a first pipe member 1 serving as an inserted pipe portion. A partially spherical inner circumferential surface 3a formed at one end of a second pipe member 3, which serves as the socket pipe portion, is slidably fitted to the partially spherical outer circumferential surface 1d of the spherical pipe portion 1A of the first pipe member 1. On the other hand, a catch member 32 provided with a partially spherical sliding surface that slides against the partially spherical outer circumferential surface 1d of the spherical pipe portion 1A of the first pipe member 1 is fixed to a flange portion 3K of the second pipe member 3 with bolts 33 and nuts 34.
In type (A), a portion of the limiting groove 4 formed on the inner circumferential surface of the spherical ring member 2 is open toward the flow path inside the pipe from the front end of the first pipe member 1, forming a ring-shaped cavity portion S1. Moreover, a ring-shaped cavity portion S2 formed by one end surface of the spherical ring member 2 and the tapered inner circumferential surface 3b connected to the partially spherical inner circumferential surface 3a of the second pipe member 3 is open toward the flow path inside the pipe. In type (B) on the other hand, the inner circumferential surface of the partially spherical pipe portion 1A of the first pipe member 1 is open toward the flow path inside the pipe, forming a ring-shaped cavity portion S3. Moreover, a ring-shaped cavity portion S4 formed by the partially spherical inner circumferential surface 3a of the second pipe member 3 and the front end of the partially spherical pipe portion 1A is open toward the flow path inside the pipe.
Therefore, even though it may not affect the intended bendability of the first pipe member and the second pipe member, if used for wastewater piping of sewers, it is not possible to completely avoid the deposition of sludge and grime in the cavity portions that open inward in radial direction at the location where the pipe members 1 and 3 are joined together. Moreover, if used for clean water piping of tap water, the flow resistance tends to increase at the cavity portions that open inward in radial direction at the location where the pipe members 1 and 3 are joined together.
As a method for preventing deposition of sludge and grime and impediments to the flow volume in type (A), there is the method of fitting a ring-shaped padding member 30 made of rubber into the limiting groove 4 of the spherical ring member 2, as shown in FIG. 13. And for type (B), there is the method of fastening a ring-shaped padding member 31 made of rubber to the inner circumferential surface of the partially spherical pipe portion 1A of the first pipe member 1, as shown in FIG. 14. But in either case, it is not possible to completely fill the cavity portion formed in the range over which the partially spherical outer circumferential surfaces 2a and 1d on the side of the first pipe member 1 slide against the partially spherical inner circumferential surface 3a of the second pipe member 3. Therefore, these measures do not sufficiently attain the effect of preventing the deposition of sludge and grime or the effect of lowering flow impediments.
In view of the above problems, it is a main object of the present invention to present a flexible pipe joint that effectively suppresses the deposition of sludge and grime as well as impediments to the flow volume while ensuring the intended bendability due to relative sliding of a partially spherical outer circumferential surface of a first pipe member and a partially spherical inner circumferential surface of a second pipe member.